Hello I am Sociocat on NA servers and I main tahm kench. I believe he is the most broken champion in the game right now and has no lane counters so he is among the safest characters to pick too. I played nothing but him for months and ended the 2021 season with a 59% winrate with over 300 games, most of them ranked.

Tahm Kench is an extremely safe top laner that is not banned enough for his threat level in lane. His abilities are all both very aggressive and very defensive making him able to 1v1 any character up to mid game. His downfall is that he is a beast up until 25 to 30 minutes into the game when the enemy has tank shredding items and CC. At that point his value changes from being an engager to supporting your own adc as a meat shield and ulting them if an assassin jumps onto them.

This way of playing tahm kench makes him the most brainless champion in the game as long as you follow the guide and learn the few tricks Tahm has.
Grasp of the Undying
this rune is required because it supports Tahms extended fighting ability with its extra damage and healing. It is the best keystone for Tahm Kench.

Shield bash
Shield bash on Tahm Kench is more important than any other rune. This rune is abused more on Kench than any other champion. Its benefits are extra armor and magic resistance when his shield is up and extra damage whenever he uses his shield ability. this synergizes best because Kench has a 3 second cooldown on his shield ability, so he can have that bonus armor and mr all the time.